1. Field of the Invention
The present invention relates to a printing device. More specifically, the present invention discloses a printing device with an improved method for positioning the print head so as to speed up the overall printing process.
2. Description of the Prior Art
One of the most common of printing methods today for printers is the use of a print head that moves left and right along a print track. Please refer to FIG. 1. FIG. 1 is a partial perspective view of a print head 10 slidably disposed along a print track 12 of a printer 5. The print head 10 slides left and right on the print track 12, along the direction of arrow RL. Rollers 14 both secure paper 7 under the print head 10, and increment the paper 7 in successive steps past the print track 12. With each pass of the print head 10, the print head 10 leaves a swath of pixels on the paper 7, and the paper 7 is incremented forward by a predetermined amount that is equal to the printing height of the print head 10. Each pass of the print head 10 is termed a xe2x80x9cprint swathxe2x80x9d, and the print head 10 traces a succession of print swaths across the paper 7 to finish a printing operation. The print swaths stack atop each other to fully cover all of the printed portions of the paper 7. Note that a print swath is not necessarily equal to a printed line of text. Depending upon the relative heights of the line of text and the printing height of the print head 10, several print swaths may be required to cover a line of text, or the print swath may cover more than just a single line of text in one print swath.
The print swaths of early printers rigorously covered every portion of the paper 7, scanning left-to-right, much as we read text. The resulting print swaths are indicated in FIG. 2. FIG. 2 is a diagram of print swaths of an early printer. The arrows indicate the direction and length of travel of the print head 10 as the print head 10 forms pixels on the paper 7. The shaded portion 16 indicates the actual extents of the printed region of the paper 7. Clearly, a great deal of time is wasted moving the print head 10 from the right side of the paper 7 to the left side to begin a print swath. Additional time is wasted by causing the print head 10 to traverse beyond the end points of the printed region 16.
A substantial savings in printing time was achieved by having the print swaths parse the paper 7 in an alternating fashion from left-to-right and right-to-left. This is indicated in FIG. 3. FIG. 3 is a diagram of print swaths of a second prior art printer. With the print swaths of FIG. 3, the print head 10 no longer behaves like the carriage return of an old-fashioned typewriter, but instead prints when traveling both to the left and to the right. This significantly decreased the amount of time required to complete a printing operation. However, the print head 10 still continues to cover the entire left and right extents of the paper 7, thus overshooting the actual printed region 16, which results in wasted time.
With the most recent advance in print head 10 positioning logic, the print head 10 no longer moves beyond the extents of the actual printing region, which is shown in FIG. 4. FIG. 4 is a diagram of print swaths of a third prior art printer. It appears that this must be the quickest method to perform a printing operation, as it minimizes wasted movement of the print head 10.
The above would seem to be the end of the story. However, under slightly more scrutiny, it becomes clear that even the above method is somewhat wasteful of time. Please refer to FIG. 5. FIG. 5 is a diagram showing print regions 20 and 22 covered by a printer using the print method of FIG. 4. The two print regions, 20 and 22, are shown covered by print swaths 21 and 23, respectively. Print swath 23 is on a line below that of print swath 21. The print head 10 scans from the left of print region 20 to the right of print region 20, then continues moving to the rightmost edge of print region 22. The paper 7 is advanced, and then the print head 10 scans from the right of print region 22 to the left of print region 22. As the print head 10 uses a fixed, alternating cycle of left-to-right and right-to-left movement, the print head 10 must traverse through region 24, performing no useful printing function, to position itself on the right side of print region 22. Time would clearly be saved if the print head 10 printed both swaths 20 and 22 in the same left-to-right manner, with the paper 7 advancing when the print head 10 was between the two print regions 20 and 22. In this case, the print head 10 would then have to traverse through the smaller distance of region 25.
It is therefore a primary objective of this invention to provide a printer with an improved print head positioning method to speed up a printing process.
The present invention, briefly summarized, discloses a printer having a print path disposed along a left-and-right direction, a driving system for moving a print head left or right along the print path, a control circuit for controlling the driving system, and a look-ahead system. The print head is used to perform a printing operation that forms at least one pixel on a media in a print swath. The look-ahead system determines a plurality of different paths that cover at least three print swaths, and computes a print time required by the driving system to cover each path. The look-ahead system then selects a path having the shortest print time, and the control system directs the driving system to follow this path.
It is an advantage of the present invention that by having a look-ahead system that computes a plurality of paths to cover at least the next three print swaths, the print head will always follow the optimal path to finish a printing operation. This results in a significant reduction in the time required to complete the printing operation.
This and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings.